In this section, we employ the method of multiple scales [1]} to obtain an approximate analytical solution of Equation (REF ). As aforementioned, and shown in Figure REF , there are two possible steady-state motions. Those that are confined to the potential well and known as intra-well oscillations and those that span the two potential wells and known as the inter-well motions. We first obtain analytical approximations of the motion trajectories within one potential well, then we seek approximate solutions that govern the inter-well motions.
